1. Field of the Invention
The present invention relates to a method of and a system for bending a sheet of glass after the sheet of glass is heated in a heating furnace and delivered out of the heating surface, and more particularly to a method of and a system for bending a sheet of glass whose heating temperatures have been uniformized over its entire surface area before the step of bending the sheet of glass.
2 Description of the Relevant Art
Heretofore, there were basically two methods of bending sheet glass. According to one method, a sheet of glass is bent within a heating furnace. The other method is directed to the bending of a sheet of glass outside of a heating furnace. According to the latter method, a bending device is disposed adjacent to the outlet of a tunnel-shaped heating furnace. The sheet of glass is fed into the heating furnace and then heated while being conveyed through the heating furnace. The heated glass sheet is delivered horizontally out of the heating furnace, and positioned between upper and lower mold members of the bending device. Thereafter, the glass sheet is pressed to shape by the upper and lower mold members.
The method of bending sheet glass outside of the heating furnace suffers the following problem: Even if the glass sheet is evenly heated within the heating furnace, when the glass sheet is delivered out of the heating furnace, the leading and trailing ends of the glass sheet are cooled for different periods of times before the glass sheet reaches the pressing position in the bending device. For example, when the glass sheet is heated to 650.degree. C. in the heating furnace, it is cooled at a rate of 6.2 degrees/second if its thickness is 3.5 mm, and at a rate of 6.6 degrees/second if its thickness is 3.1 mm. At the time the glass sheet is bent to shape, the leading and trailing ends thereof have different temperatures which may depend on surrounding conditions. The different temperatures then lead to different viscosities of the leading and trailing ends, resulting in possible cracks in the glass sheet when it is pressed or cooled, or inaccurate bent configurations.